Vancomycin-resistant enterococci in intensive-care hospital settings: Transmission dynamics, persistence, and the impact of infection control programs

Vancomycin-resistant enterococci (VRE) recently have emerged as a nosocomia l pathogen especially in intensive-care units (ICUs) worldwide, Transmissio n via the hands of health-care workers is an important determinant of sprea d and persistence in a VRE-endemic ICU, We describe the transmission of nos ocomial pathogens by using a microepidemiological framework based on the tr ansmission dynamics of vector-borne diseases, By using the concept of a bas ic reproductive number, R-0, defined as the average number of secondary cas es generated by one primary case, we show quantitatively how infection cont rol measures such as hand washing, cohorting, and antibiotic restriction af fect nosocomial cross-transmission. By using detailed molecular epidemiolog ical surveillance and compliance monitoring, we found that the estimated ba sic reproductive number for VRE during a study at the Cook County Hospital, Chicago, was approximately 3-4 without infection control and 0.7 when infe ction control measures were included. The impact of infection control was t o reduce the prevalence from a predicted 79% to an observed 36%. Hand washi ng and staff cohorting are the most powerful control measures although thei r efficacy depends on the magnitude of R-0. Under the circumstances tested, endemicity of VRE was stabilized despite infection control measures, by th e constant introduction of colonized patients. Multiple stochastic simulati ons of the model revealed excellent agreement with observed pattern. In con junction with detailed microbiological surveillance, a mathematical framewo rk provides a precise template to describe the colonization dynamics of VRE in ICUs and impact of infection control measures. Our analyses suggest tha t compliance for hand washing significantly in excess of reported levels, o r the cohorting of nursing staff, are needed to prevent nosocomial transmis sion of VRE in endemic settings.